Reactor for chemical conversion of a feedstock in the presence of a diluent, with heat inputs and feedstock/catalyst cross-circulation

ABSTRACT

A reactor with integrated heat for carrying out a chemical conversion process in the presence of a gaseous diluent supplied through one or more ports at the upper and/or lower ends of a catalytic bed through which a feed moves substantially horizontally, and a process for converting a feed, such as a hydrocarbon feed in the reactor.

The chemical, petroleum and petrochemical industries employ manyendothermic chemical reactions, for example cracking reactions,dehydrogenation reactions or hydrocarbon reforming reactions.

Certain of those reactions are reversible and limited by a thermodynamicequilibrium. In that case, the cooling occurring in the catalytic beddue to the endothermic nature of the reaction limits the reactantconversion.

One method for obtaining a high conversion consists of introducingheating surfaces into the catalytic bed, or using a plurality ofcatalytic beds separated by zones for re-heating the reaction fluid.

Frequently, a diluent is added to the feed to reduce its partialpressure and/or protect the catalyst. Diluents are generally selectedfrom the group formed by steam, nitrogen, hydrogen and mixtures thereof.

In many cases, in particular for hydrocarbon dehydrogenation, thecatalyst is at least partially deactivated during the reaction, forexample by coking, and must be extracted, continuously or at distincttime intervals, and replaced by new or regenerated catalyst.

Processes such as catalytic hydrocarbon reforming are known in which thereaction feed successively traverses a plurality of catalytic bedreactors, with intermediate re-heating between the reactors tocompensate for cooling of the reaction fluid due to the endothermicnature of the reaction. The catalyst flows from one reactor to another,as a co-current or as a counter-current to the feed plus hydrogen-richdiluent before being regenerated and recycled. The catalyst is usedefficiently and homogeneously coked before being regenerated.

The invention concerns a reactor for chemical conversion of a feed, saidchemical conversion reactor containing a substantially verticalcatalytic bed between an upper end and a lower end for chemicalconversion of a feed in the presence of a gaseous diluent, andcomprising, in combination:

-   -   close to the upper end of said reactor, at least one means for        introducing a solid catalyst;    -   means for introducing and evacuating said feed allowing its flow        in a substantially horizontal manner through the catalytic bed;    -   in the proximity of the lower end of said reactor, at least one        means for extracting catalyst;    -   at least one means for heating said feed plus added diluent,        said means being internal to the reactor and traversed by said        feed plus added diluent in the absence of catalyst, and        separating the catalytic bed into a portion upstream of and a        portion downstream of said heating means relative to the        direction of flow of said feed;        said reactor comprising at least one means for introducing a        stream of said gaseous diluent substantially in the proximity of        at least one of the upper and/or lower ends of said upstream        portion of the catalytic bed, to at least reduce by-passing of        said heating means by said feed plus added diluent.

Preferably, the means for introducing a stream of gaseous diluent isselected from the group formed by means with a capacity sufficient toprevent any by-passing of the heating means.

Typically, the means for introducing gaseous diluent is locatedsubstantially in the proximity of the upper end of the upstream portionof the catalytic bed. It is also possible to introduce a stream ofgaseous diluent in the proximity of the lower end of the upstreamportion of the catalytic bed to reduce or prevent by-passing of theheating means at the bottom of the catalytic bed.

The invention also provides a process for chemical conversion of a feedusing a reactor as described above.

In particular, the conversion process is applicable to a hydrocarbonfeed.

More particularly, the process of the invention is a process forcatalytic dehydrogenation of a paraffinic hydrocarbon feed.

The reactor can be a reactor-exchanger with heating surfaces immersed inthe catalytic bed; it can also comprise a plurality of catalytic bedsseparated by non-catalytic zones for heating the reaction feed. In eachof these zones, the reaction feed traverses a heat exchanger, suppliedwith a heat transfer fluid.

Heat transfer fluids that can be used include pressurised steam, forexample between 0.5 MPa and 1.20 MPa, preferably between 0.6 MP and 1MPa absolute, limits included, hydrogen or a hydrogen-containing gassuch as a hydrogen-rich recycle gas, such as that used in certainprocesses to dilute the reaction feed to protect the catalyst. It isalso possible to use the unconverted feed itself, or liquids such asmolten salts or liquid sodium.

The differentiated catalyst extraction means is normally selected fromthe group formed by continuous and discontinuous extraction means.

Preferably, the catalytic bed comprises a plurality of catalytic zonesseparated by non-catalytic zones for heating the feed.

In a preferred feature of the invention, the most upstream catalystextraction means differs from the furthest downstream extraction meansin its lower extraction capacity (the concepts of upstream anddownstream being with respect to the direction of flow of the feed).

The invention also proposes a process for chemical conversion of a feedusing a reactor as described above.

Typically, the feed is a hydrocarbon feed, often with an added diluent(for example steam, hydrogen, nitrogen or a mixture of these gases).

In a particular implementation of the invention, the chemical conversionprocess is a process for catalytic dehydrogenation of a paraffinichydrocarbon feed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1: Illustrates a reactor in accordance with the invention withmeans for introducing diluent in an upper end and a lower end of thereactor.

FIG. 2: Illustrates a reactor in accordance with the invention withmeans for introducing diluent in a lower end of the reactor.

FIG. 3: Illustrates a reactor in accordance with the invention withmeans for introducing diluent in an upper end and a lower end of thereactor.

We shall now refer to FIG. 1, which is a non-limiting representation ofa reactor R in accordance with the process of the invention.

The reaction feed is introduced into reactor R via a line 1; ittraverses, in succession, a catalytic bed 3 a, then a heat exchanger 4a, then a second catalytic bed 3 b, then a second heat exchanger 4 b,then a third and last catalytic bed 3 c, before leaving the reactor viaa line 2. The catalyst is introduced into the reactor at the headthereof via a line 9. It is distributed into the three catalytic beds 3a, 3 b, 3 c in which they flow under gravity in downflow mode. Eachcatalytic bed has a separate hopper for evacuating the catalyst: 7 a forbed 3 a, 7 b for bed 3 b and 7 c for bed 3 c.

Extraction valves 8 a, 8 b, 8 c at the bottom of each of the catalyticbeds can separately extract used catalyst flowing in each of thecatalytic beds in series. The catalyst is evacuated via lines 80 a, 80 band 80 c.

In a single catalyst bed reactor, extraction valves 8 a–c are replacedwith a single extraction valve 8 and lines 80 a–c are replaced withsingle line 80 as can be seen on FIGS. 2 and 3.

Heat exchangers 4 a and 4 b are fed by heat transfer fluid introducedvia lines 5, 5 a and 5 b, this fluid leaving the exchanger via lines 6a, 6 b and 6.

At the upper portion of beds 3 a and 3 b, flow of gaseous diluent isintroduced via lines 10, 10 a and 10 b. The function of this gas is toprovide a barrier gas to prevent feed passing from bed 3 a to bed 3 band by-passing exchanger 4 a, and similarly preventing feed passing frombed 3 b to bed 3 c and by-passing exchanger 4 b. By-pass is highlydeleterious to the overall conversion of the feed as the portion of feedthat by-passes the heating means is only slightly converted.

At a lower portion of the bed(s), flow of gaseous diluent is introducedvia lines 11, 11 a and 11 b as can be seen in FIGS. 2 and 3.

Typically, this gas can be a diluent for the feed, for example steam ora hydrogen-rich recycle gas.

The unit functions as follows.

The feed, pre-heated to the reaction temperature, traverses the threecatalytic beds (or zones) 3 a, 3 b, 3 c in series, with two intermediatere-heating steps.

The catalyst, introduced via line 9, is extracted continuously ordiscontinuously via lines 80 a, 80 b, 80 c.

In the reactor, in accordance with the invention, the catalyst flowingin bed 3 c is preferably renewed more rapidly than that in bed 3 a.Typically, the catalyst ages more rapidly and deactivates and cokes morerapidly at the end of the reaction zone, i.e., in the downstream bed 3 cmore than in the upstream bed 3 a. Preferably, 3 c is renewed morerapidly than 3 b, which is itself renewed more rapidly than bed 3 a.

The invention thus enables the catalyst to be used efficiently, whichcatalyst is extracted in a relatively constant state of deactivation.

When operation is continuous, valves 8 a, 8 b, 8 c can be used to adjustthe differentiated catalyst extraction.

When operation is discontinuous, varying quantities of catalyst can beextracted at intervals depending on the catalytic zones (higherextraction rates in the downstream zones in the direction of feed flow).

It is also possible to carry out more frequent catalyst extraction inthe downstream zone 3 c than in zone 3 b and/or in zone 3 b than in zone3 a. It is also possible to modulate the frequency and quantities ofcatalyst extracted.

Finally, it is possible to carry out limited extraction of the usedcatalyst (for example 10% to 33% by volume of each bed) or to renew theentire volume of an individual bed (or zone): 3 a, 3 b or 3 c. In thiscase, the catalyst in zone 3 c is preferably renewed more frequentlythan that in zone 3 a.

The reactors of the invention can contain 2 to about 20 catalytic zonesseparated by heat exchange zones.

The reaction fluid can also be introduced laterally and flowhorizontally, as a crosswise current to the feed.

It is possible to use thin beds, for example 5 to 10 cm thick, or ofmedium thickness, for example between 10 and 80 cm, and if the processdemands it, low or high space velocities (for example 10 to 250 h⁻¹).The temperatures depend on the process but are frequently in the range250° C. to 950° C., preferably between about 400° C. and about 700° C.These values do not limit the invention.

The scope of the invention also encompasses the case wherein there isbut a single catalytic bed, or beds in parallel, with a crosswisefeed/catalyst flow.

The reactor of the invention can carry out chemical conversion of a feedin the presence of a catalyst while providing each of the catalyticzones with the necessary amount of heat. It also enables the at leastpartially deactivated catalyst to be extracted in a differentiatedmanner.

The reactor of the invention can maintain a high catalytic activityand/or productivity for the desired product.

The invention can in particular be employed for hydrocarbon reforming,for dehydrogenating ethylbenzene, and for dehydrogenating paraffins suchas propane, n-butane, isobutane, primarily linear paraffins containing10 to 14 carbon atoms, and for the production of olefins for theproduction of alkylbenzenes, or for other chemical reactions.

1. A reactor for chemical conversion in the presence of a gaseousdiluent, containing a substantially vertical catalytic bed between anupper end and a lower end and comprising, in combination: close to theupper end of said reactor, at least one means for introducing a solidcatalyst; means for introducing and evacuating said feed allowing itsflow in a substantially horizontal manner through the catalytic bed; inthe proximity of the lower end of said reactor, at least one means forextracting catalyst; at least one means for heating said feed plus addeddiluent, said means being internal to the reactor and traversed by saidfeed plus added diluent in the absence of catalyst, and separating thecatalytic bed into an upstream portion and a portion downstream of saidheating means relative to the direction of flow of said feed; whereinthe reactor comprises at least one means for introducing a stream ofsaid gaseous diluent substantially in the proximity of at least one ofthe upper and/or lower ends of said upstream portion of the catalyticbed, to at least reduce by-passing of said heating means by said feedplus added diluent.
 2. A reactor according to claim 1, in which themeans for introducing a stream of gaseous diluent is selected from thegroup formed by means with a capacity sufficient to prevent by-passingof the heating means.
 3. A reactor according to claim 1, in which themeans for introducing gaseous diluent is located substantially in theproximity of the upper end of the upstream portion of the catalytic bed.4. A reactor according to claim 1, wherein the gaseous diluent isintroduced substantially in the proximity of the upper and lower ends ofthe upstream portion of the catalytic bed.
 5. A reactor according toclaim 1, wherein the gaseous diluent is introduced substantially in theproximity of the upper end of the upstream portion of the catalytic bed.6. A reactor according to claim 1, wherein the gaseous diluent isintroduced substantially in the proximity of the lower end of theupstream portion of the catalytic bed.
 7. A reactor according to claim1, wherein the catalytic bed is separated into upstream and downstreamportions with respect to direction of flow of the feed by separators orthe catalytic bed has separate hoppers for said upstream and downstreamportions.
 8. A reactor according to claim 5, wherein the catalytic bedis separated into upstream and downstream portions with respect todirection of flow of the feed by separators or the catalytic bed hasseparate hoppers for said upstream and downstream portions.
 9. A reactoraccording to claim 1, wherein the catalytic bed is a single catalyticbed which is separated by zones for heating into at least an upstreamand downstream portions with respect to direction of flow of the feed.10. A reactor according to claim 4, wherein the catalytic bed is asingle catalytic bed which is separated by zones for heating into atleast an upstream and downstream portions with respect to direction offlow of the feed.
 11. A reactor according to claim 6, wherein thecatalytic bed is a single catalytic bed which is separated by zones forheating into at least an upstream and downstream portions with respectto direction of flow of the feed.
 12. A reactor according to claim 7,wherein a separate catalyst extraction port is provided for each ofseparated upstream and downstream portions of the catalytic bed.
 13. Areactor according to claim 1, wherein the means for introducing the feedand the diluent are separate from each other.
 14. A reactor for chemicalconversion in the presence of a gaseous diluent, containing asubstantially vertical catalytic bed between an upper end and a lowerend and comprising close to the upper end of the reactor a solidcatalyst introduction port, a feed introduction into the reactor and afeed removal port configured to allow feed flow in a substantiallyhorizontal manner through the catalytic bed, in the proximity of thelower end of the reactor, a catalyst extraction port, a catalytic bedheating element which is internal to the reactor and which is traversedby feed and which separates the catalytic bed into an upstream portionand a portion downstream of said heating means relative to the directionof flow of said feed, and at least one gaseous diluent streamintroduction port, substantially in the proximity of at least one of theupper and/or lower ends of said upstream portion of the catalytic bed,capable of reducing by-passing of the heating element by the feed plusdiluent.
 15. A reactor according to claim 14, wherein the feedintroduction and diluent stream introduction ports are separate fromeach other.
 16. A reactor according to claim 14, wherein the at leastone gaseous diluent stream introduction port is substantially in theproximity of the upper end of said upstream portion of the catalyticbed.